Pulse controlled solenoid valve

Abstract

A pulsed controlled solenoid flow control valve suitable for use in a closed vapor cycle air conditioning system is disclosed. A pulsewidth modulated control signal is generated for cyclically opening and closing the flow through the expansion valve. The duty cycle of the pulsed control signal determines the average flow rate through the valve. An exponential response control curve is used in conjunction with an integrator offset to obtain a single set point control operating point for all flow rates through the valve, where a given change in the second superheat of the evaporator produces the same percentage change in flow rate regardless of the flow rate.

What is claimed is: 
     
       1. In combination with a closed vapor cycle refrigeration system including in connected closed loop sequence, a compressor, a condenser, a solenoid actuated expansion valve and an expansion evaporator, improved electronic expansion valve apparatus, comprising: (a) a means for sensing the superheat of the expansion evaporator and producing an electrical signal level indicative thereof;   (b) a converting means connected to said sensing means and producing from the electrical signal level an on-off modulated signal whose duty cycle is representative of the required flow rate of liquid refrigerant through said valve; and   (c) a means responsive to said on-off modulated signal for slowly opening and closing said valve without imparting any substantial pressure shockwaves to the liquid refrigerant, said expansion valve being modulated operated by said converting means and said means for slowly opening and closing said valve from an open position to a closed position for each cycle of the on-off modulated signal to produce an average refrigerant flow rate therethrough in accordance with the duty cycle of said on-off modulated signal.   
     
     
       2. An electrically-operated solenoid expansion valve for controlling refrigerant flow into the evaporator coil of a closed vapor cycle refrigeration system, comprising: (a) a valve closure means having a closure for opening and closing fluid flow from the condenser coil of the refrigeration system to said evaporator coil,   (b) an electrical control means for alternately operating said valve closure means opened and closed over a period of time to maintain the fluid in said evaporator coil substantially in its liquid state, and   (c) a means for slowly opening and closing said closure means so as not to impart a substantial pressure shockwave into said fluid with each opening and closing of said valve.   
     
     
       3. An electrically operated expansion valve in accordance with claim 2, wherein said valve closure means is a shear acting closure mechanism. 
     
     
       4. An electrically operated expansion valve in accordance with claim 2, wherein said valve closure means includes magnetic means for operating said closure in linear fashion through at least a substantial range of closure movement. 
     
     
       5. A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said valve including an on-off modulator responsive to the superheat of said refrigerant in said evaporator for generating a variable duty cycle on-off modulated solenoid control signal, and a means responsive to said on-off modulated signal for slowly opening and closing said valve without imparting any substantial pressure shockwaves to the liquid refrigerant, said solenoid control signal alternately energizing and deenergizing said solenoid for each cycle of said control signal to cycle said valve from a first flow rate position to a second flow rate position thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant. 
     
     
       6. The valve of claim 5 wherein said first flow rate position results in a fully open maximum flow rate therethrough, and said second flow rate position results in a fully closed zero flow rate therethrough, said average flow rate being determined by the duty cycle of said solenoid control signal. 
     
     
       7. The valve of claim 5 wherein said means for slowly opening and closing said valve further includes a closure rate control means controlling the rate of change in flow rate positions of said valve between said first and said second flow rate positions, and vice versa, thereby to minimize any pressure shockwaves in said refrigerant on opening or closing of said valve. 
     
     
       8. The valve of claim 6 wherein said means for slowly opening and closing said valve further includes a closure rate control means for controlling the rate of change in flow rate positions of said valve between said fully open and said fully closed positions, and vice versa, thereby to minimize any pressure shockwaves in said liquid refrigerant on opening or closing of said valve. 
     
     
       9. The valve of claims 7 or 8 wherein said closure rate control means is an electronic circuit which decreases the slope of the pulse edges in the on-off solenoid control signal. 
     
     
       10. The valve of claims 6, 7 or 8 wherein said valve further includes: (a) a superheat sensing means coupled to said evaporator for sensing the instantaneous superheat of the refrigerant in said evaporator;   (b) a superheat setting means for selecting a desired superheat operating set point for said refrigerant; and   (c) a differential amplifier means responsive to the sensed instantaneous superheat and said desired superheat operating set point for generating a duty cycle control signal to said on-off modulator as a function of the difference between said sensed and said superhet operating set point.   
     
     
       11. The valve of claim 10 wherein said superheat sensing means includes: (a) an inlet temperature sensor for sensing the temperature of said refrigerant at the inlet end of said evaporator; and   (b) an outlet temperature sensor for sensing the temperature of said refrigerant at the outlet end of said evaporator, the difference between said inlet and said output temperature representative of the instantaneous superheat of said refrigerant.   
     
     
       12. The valve of claim 10 wherein said differential amplifier means includes: (a) a first differential amplifier responsive to the sensed superheat and the superheat operating set point for generating an operating point control signal representative of the difference between the sensed superheat and the superheat operating set point;   (b) an integration means responsive to the operating point control signal for generating an operating point shift control signal as a function of the time average of the difference between the instantaneous sensed superheat and the superheat set point; and   (c) a second differential amplifier responsive to the operating point control signal and the operating point shift control signal for generating the duty cycle control signal to said on-off modulator, the operating point shift control signal dynamically shifting the effective operating set point of the valve without changing the single superheat operating set point of said superheat setting means.   
     
     
       13. The valve of claim 12 wherein said integration means comprises an analog amplifier integrator circuit. 
     
     
       14. The valve of claim 12 wherein said integration means is a digital integrator comprising: (a) a clock for generating timing pulses;   (b) a comparator circuit responsive to the operating point control signal and a threshhold voltage for generating an up/down control signal;   (c) an up/down counter responsive to the timing pulses and the up/down control signal, said counter counting up when the operating point control signal is above the threshhold and counting down when the operating point control signal is below the threshhold; and   (d) a digital-to-analog converter for converting the count in said counter into an analog voltage as the operating point shift control signal.   
     
     
       15. The valve of claim 8 further including a driving amplifier circuit responsive to the output from said on-off modulator circuit for providing power driving signals to said solenoid. 
     
     
       16. The valve of claims 7 or 8 further including a low ambient start-up means responsive to the presence of liquid refrigerant at the inlet end of said expansion valve for overriding normal operations of said valve and maintaining said expansion valve open for refrigerant flow therethrough when liquid refrigerant is not present, said low ambient start-up means returning control for normal operations of said valve when liquid refrigerant is present. 
     
     
       17. The valve of claim 16 wherein said low ambient start-up means comprises: (a) a first temperature sensor coupled proximal to the inlet end of said expansion valve, said first sensor generating a voltage representative of the temperature of the liquid refrigerant from said condensor;   (b) a second temperature sensor coupled proximal to the outlet end of said expansion valve, said second means generating a voltage representative of the temperature of the expanding liquid refrigerant into the inlet end of said evaporator;   (c) a comparator circuit responsive to the voltages from said first and second temperature sensors for generating a low ambient start signal when the temperature differential between said first and second sensors is less than a temperature threshold; and   (d) a clamping means responsive to the low ambient start signal for overriding normal control of said expansion valve and maintaining said expansion valve open for refrigerant flow therethrough until the temperature differential between said first and second sensors is greater than the temperature threshold indicating expansion of liquid refrigerant through said valve.   
     
     
       18. The valve of claim 17 further including an ambient air temperature sensing means responsive to the ambient air temperature for disabling said low ambient start up means from controlling said expansion valve when said ambient air temperature is below a minimum temperature, said ambient temperatue sensing means disabling said valve at the operating conditions then present so that when the ambient air temperature exceeds the minimum temperature, said valve may resume normal operations with the conditions present when the air temperature last dropped below the minimum. 
     
     
       19. The valve of claims 7 or 8 further including a flood detector means responsive to the outlet-to-inlet temperature differential across said evaporator coil for throttling down the flow rate through said expansion valve when the temperature differential is less than a temperature threshold, said flood detector means generating a throttling control signal representative of a lower heat load condition on said evaporator coil to said valve as long as the temperature differential is less than said temperature threshold, said valve resuming normal operation from the throttled-down condition when said temperature differential is greater than said temperature threshold. 
     
     
       20. The valve of claim 19 wherein said flood detector means comprises: (a) a first temperature sensor responsive to the temperature of the refrigerant at the inlet end of said evaporator;   (b) a second temperature sensor responsive to the temperature of the refrigerant at the outlet end of said evaporator; and   (c) a first comparator means responsive to said first and second temperature sensors for generating a flood condition signal when the temperature differential between said first and second sensors is less than said temperature threshold, said flood condition control signal representing a reduced heat load demand condition on said evaporator and which is applied to said valve to effect throttling down of the flow of liquid refrigerant through said expansion valve, said comparator means returning normal control to said expansion valve when said temperature differential between said first and second sensors is greater than said temperature threshold.   
     
     
       21. The valve of claims 19 or 20 further including a second comparator means responsive to the absolute temperature of said liquid refrigerant at said inlet end of said evaporator and to a maximum operating refrigerant temperature signal for outputting to said controller means a maximum operating temperature control signal to throttle down the flow of refrigerant through said expansion valve when the temperature of said liquid refrigerant at the inlet end of said evaporator coil is greater than the maximum operating refrigerant temperature, said comparator means returning normal control to said expansion valve when said evaporator inlet temperature is less than the maximum refrigerant temperature. 
     
     
       22. The valve of claim 21 further including an OR gate responsive to the flood condition control signal and the maximum operating temperature control signal for outputting to said controller means a fast shut down control signal to effect throttling down of the flow through said expansion valve when either the flood condition control signal or the maximum temperature signal indicates, respectively, that a flood condition exists in said evaporator coil or that the absolute temperature of the liquid refrigerant into said evaporator coil is above a maximum limit. 
     
     
       23. The valve of claims 7 or 8 further including a low refrigerant detection means responsive to the percent on time of said valve for generating a low refrigerant alarm signal when the percent on time of the valve exceeds a threshhold value for a period of time. 
     
     
       24. The valve of claim 23 wherein said low refrigerant detection means comprises: (a) a comparator responsive to the input signal to said on-off modulator, such input signal representative of the duty cycle of the solenoid control signal and to a duty cycle threshhold signal;   (b) a reset timer coupled to the output from said comparator for generating an output when the duty cycle of the solenoid control signal is above the threshhold value for a period of time determined by said timer; and   (c) an alarm circuit responsive to the output from reset timer to indicate a low refrigerant condition in said system.   
     
     
       25. In a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end connected to said condenser and to the inlet end of said compressor, a solenoid actuated expansion valve having an inlet and an outlet end and connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said solenoid actuated expansion valve, said refrigerant expanding as it flows through said solenoid actuated expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said solenoid actuated expansion valve, said controller circuit including an on-off modulator for generating an on-off modulated solenoid control signal whose duty cycle varies as a function of the superheat, a means responsive to said on-off modulated signal for slowly opening and closing said valve without imparting any substantial pressure shockwaves to the liquid refrigerant, and a low refrigerant detection means responsive to the duty cycle of the on-off modulated solenoid control signal for generating a low refrigerant alarm signal when the duty cycle of the solenoid control signal exceeds an upper threshold value for a period of time. 
     
     
       26. The valve of claim 25 wherein said low refrigerant detection means comprises: (a) a comparator responsive to the input signal to said on-off modulator, such input signal representative of the duty cycle of the solenoid control signal and to a duty cycle threshhold signal;   (b) a reset timer coupled to the output from said comparator for generating an output when the duty cycle of the solenoid control signal is above the threshhold value for a period of time determined by said timer; and   (c) an alarm circuit responsive to the output from reset timer to indicate a low refrigerant condition in said system.   
     
     
       27. A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said expansion valve having a movable orifice opening element responsive to a solenoid control signal for obtaining an orifice opening size, said valve having hysteresis errors in the position of said orifice opening element in response to said solenoid control signal, said valve including a means for generating a solenoid control signal having an oscillatory component whose frequency is within the response range for movement of said orifice opening element and which causes said orifice opening element to slowly move between a first position and a second position without imparting any substantial liquid shockwaves to the refrigerant, thereby eliminating said positional hysteresis errors in obtaining a desired orifice opening size. 
     
     
       28. The valve of claim 27 wherein said solenoid control signal further includes an average value component representative of a desired orifice opening size, said orifice opening element responsive to said oscillatory component moving between said first and second positions about a desired average opening size. 
     
     
       29. The valve of claim 27 wherein said oscillatory component is a square wave. 
     
     
       30. The valve of claim 29 wherein said means for oscillating said element includes a means for generating an on-off modulated control signal whose duty cycle represents a desired average flow rate through the valve, said oscillating means responsive to the on-off control signal slowly moving said orifice opening element from a closed position to an open position for each cycle of said on-off modulated control signal without imparting any substantial liquid shockwaves to the refrigerant. 
     
     
       31. The valve of claim 30 wherein the amplitude of said oscillatory component of said solenoid control signal is representative of the magnitude of the positional hysteresis error and causes no positional movement of said orifice opening element.